ImRich wrote:Yes, mine is a 2005 and works as yours does, but I'd still like to hear the details about this claim, even if to understand it was talking about an older model.

Bt Doctur wrote:Volvo uses the alt to provide voltage for the fuel pumps, bad alt = no fuel. Dumb idea and why I convert the fuel system to mercruiser type using the oil pressure switch.

@Bt Doctur can you please elaborate?

Seems like the Bt doctor doesnt have any more info regarding his comments? Probably just give up on any more info as to where he obtained this ? My 2001 starts and runs like a new engine, I can hear the electric fuel pump engage and the low oil PSI alarm comes on to tell me the switch is working prior to cranking.

Fuel injection uses the ECM to prime and run the fuel pumps both high and low pressures.The carb`d motors use the alt power to run the electric fuel pump. If the alt dies the fuel pump power also dies. Using a oil pressure switch and another "switched" power source keeps the fuel pump in operation no matter what the alt decides to do.

I located 2 8.1 manuals 1 in spanish and 1 in german and neither had the wiring. this is from a merc but should be close The fuel pump relay operated on a ground condition supplied by the ecm. Locate the fuel pump relay wiring . If there is a green wire , cut and ground it and the relay should close and power the fuel pump. If not get me the colors of the fuel pump relay wiring pin #86

Bt Doctur wrote:Fuel injection uses the ECM to prime and run the fuel pumps both high and low pressures.The carb`d motors use the alt power to run the electric fuel pump. If the alt dies the fuel pump power also dies. Using a oil pressure switch and another "switched" power source keeps the fuel pump in operation no matter what the alt decides to do.

Interesting. I would jump terminal 30 (B+ from battery/fuse?) to 87 B+ to pump and if the fuel pump has its own ground the fuel pump should energize and run? Why do the marine engine manufactures make thing so complicated? IF your ECU detects low oil pressure or high jacket water temperature It should just give you a alarm at the helm and then put you into a "limp home mode"? The diode in the circuit looks like a blocking diode which just allows current to flow in one direction, why would the alternator have to be producing current before the fuel pump gets energized? That would mean the engine has to crank and start first before the fuel pump would provide pressurized fuel to the injection system? Something is funny here. By the way, kudos for posing the wiring diagrams in your previous mails! Now I am wondering why there is a blocking diode from the relay terminal block to the engines alternator? I am thinking that terminal 85 is just a "field flashing" circuit to wake up the alternator to start producing current?

My current projects are attempting to isolate the values to eliminate/block the trouble codes and Guardian Mode applications .Way too many sensors that really are not needed . Just watch the instruments and do your normal service.Variable sensors use the 5 Vdc input ,a fixed resistance to ground, and a wiper arm that sends a voltage to the ecm.Once that "center line" value is found install a resistor bridge to eliminate the sensor and thus fool the ecm.There is a sensor in a Bravo application that prevents high rpm unless in gear. Now, if you can`t read English and you didnt read the operator manual you would know not to push the throttle lever all the way down in neutral .ya think?

If these engineers keep doing this stuff I will write a book "BOATING FOR DUMMY BOAT OWNERS WHO CAN`T READ

If you follow the current flow thru the diodes you can see what will happen at diode failure. If the alt quits you lose the fuel pump. If the starters diode quite the starter engages neither option is good. At the very least I would wire in a lead to connect directly to the battery or a 12v source to keep the fuel pump running.

Not sure about wiring the fuel pump directly into a unswitched B+ feed or directly to the battery, the pump would be energized all the time, engine running or not? All this new electronics are getting beyond my background/experience Glad we have just a ECM multi port EFI engine and everything else is mechanical, i.e. throttle, shift levers, and both a sender and switch indicating a alarm at the helm for both low oil PSI and high jacket water temps. All the new full electronic stuf is great until it stops working? Then ?

No, not hot all the time, using a oil pressure switch prevents that. The oil pressure switch operates the relay for the fuel pump. The feed for the fuel pump is a fused circuit and the feed for the relay is a switched circuit. Ign on supplies power to the switch and once oil pressure is there the switch closes and power goes to the fuel pump.

Bt Doctur wrote:Fuel injection uses the ECM to prime and run the fuel pumps both high and low pressures.The carb`d motors use the alt power to run the electric fuel pump. If the alt dies the fuel pump power also dies. Using a oil pressure switch and another "switched" power source keeps the fuel pump in operation no matter what the alt decides to do.

First, thanks for answering!

So this is an issue only for carb'ed engines?

Or do fuel injected engines also provide fuel pump power via the alternator?I'm asking as my current thinking is wondering if a slipping serpentine belt could cause a motor to die at idle speeds on a fuel injected engines.

As to a slipping belt, only is the battery voltage is very low If you look at the ECM wiring post you can see the relay is directly powered and the fuel pump is directly powered. All a ECM does is look for a ground, produce ground or monitor the variable voltage produced by the wiper or thermistor .To turn the fuel pumps on the ECM provides the ground for the circuit PROVIDED it gets the information from all the other sensors. cam, crank, dist, map, etc

Bt Doctur wrote:No, not hot all the time, using a oil pressure switch prevents that. The oil pressure switch operates the relay for the fuel pump. The feed for the fuel pump is a fused circuit and the feed for the relay is a switched circuit. Ign on supplies power to the switch and once oil pressure is there the switch closes and power goes to the fuel pump.

My thoughts =

OK, makes sense other than if your battery is low and cant turn the engine over fast enough to provide a signal to the fuel pump from the oil pressure sensor you will most likely not be able to start the engine so the alternator will start functioning to charge the starting battery and continue to run? Also, if your fuel pump pressure leaks down over time your fuel injection system would not have enough accumulated pressure to allow the injectors to open and inject the required amount of starting fuel (like a carbureted engines "choke") to actually start the engine?